The 'invisible' bridge that will cost $1 million to fix

A RUSTY 135m bridge on the Casino to Murwillumbah rail line will cost an estimated $1 million to fix as part of a rail trail proposal.

The massive steel bridge across Leycester Creek in Lismore is 135m long, and features three almost 37m long truss spans.

It is an iconic feature of the rail corridor, but is in danger of degrading beyond repair if the rusting is not stopped, according to a local engineer who recently assessed it.

The railway line in South LIsmore.Marc Stapelberg

Patrick Knight is a local civil engineer who has spent the last nine months inspecting the state of the line between Casino and Mullumbimby along with fellow engineer Norm Case.

Both men conducted their work on a pro bono basis to support the Northern Rivers Rail Trail project.

Mr Knight said the biggest cost of rail trail was the refurbishment of the bridges. Yet they are also one of the trail's biggest features.

There are 116 bridges between Casino and Mullumbimby. Some are tiny and easily repaired, while others require more serious maintenance.

The Leycester Creek bridge is one of those.

Already in a state of corrosion, Mr Knight said it would require an estimated $100,000 to conduct a proper assessment of its state.

"There is a lot of rust, particularly on the lower sections, and from an engineering point of view they are in tension. If you put a train on it, they are going to be critical," Mr Knight said.

"We believe there is enough steel left to carry the loads we're talking about (cyclists, horses, and foot traffic), but we need to do corrosion protection so it doesn't get any worse."

"The tricky part of it is is to assess it properly, you need to scaffold the entire bridge so inspectors can look at these things safely.

MASSIVE: The Leycester Creek bridge looking from North Lismore, near the Italo Club.JASMINE BURKE

"We're estimating it's going to cost somewhwere in the vicinity of $1 million to inspect it and apply corrosion resistance to it."

But Mr Knight said he believed it was worth the effort.

"It's very historical and of good heritage value... it's just a fantastic bridge, it would be great to walk or ride across there, the Lismore community would just love it."

"Even if it's not used for a rail trail... just for the heritage value someone needs to do something about it... if no one takes ownership of it and does anything about it it will just rust to bits."

It is just one of 20 bridges between Lismore and Eltham which are estimated to cost more than $10 million to refurbish according to Mr Knight's costings.

At 135m long the Leycester Creek bridge is not actually the longest bridge along the rail corridor. There is a 225m bridge west of Lismore near Tuncester, and a 222m bridge running over a floodplain at Eltham. But both of these are much lower than the Leycester Creek bridge, and don't pass over a large body of water.

The Leycester Creek bridge is made from steel, but the vast majority of bridges on the rail corridor are timber.

The railwayline near Woodlawn.Marc Stapelberg

Mr Knight was the Shire engineer at Kyogle Council for 11 years and the experience he gained there on the council's 100-plus timber road bridges was invaluable

"I'm fairly familiar with what it takes to restore timber bridges," he said.

He said most of the timber bridges were rotting beyond repair and given they were built from old-growth hardwood it was impossible to replace them with the original materials used.

He also said the tradesmen who had proper expertise in timber bridge building were in short supply these days.

The railway bridge near the Lismore Turf Club.Marc Stapelberg

Instead, it is suggested to replace the rotting wood with galvanised steel.

"The geometry of them will be much the same," Mr Knight said.

To do accurate costings, the team divided the corridor up into sections between the main towns and villages.

In total, they have estimated it would cost $73.4 million to refurbish the bridges and build the trail from Casino to Crabbes Creek, which would connect it to the Tweed rail trail (which has already received funding).

This estimate included road base and surfacing for the trail, installing safety balustrades and flooring on the bridges, and refurbishing the bridges.

The team has noted that the final costing could be downgraded if it is decided to bypass some of the lower bridges, but the bigger ones were iconic landmarks and part of the essential attraction of the project.